The present invention relates to gas generant compositions that upon combustion produce a relatively smaller amount of solids and a relatively abundant amount of gas. It is an ongoing challenge to reduce the amount of solids and increase the amount of gas thereby decreasing the filtration requirements for an inflator. As a result, the filter may be either reduced in size or eliminated altogether thereby reducing the weight and/or size of the inflator. Additionally, reduction of combustion solids provides relatively greater amounts of gaseous products per gram or unit of gas generating composition. Accordingly, less gas generant is required when greater mols of gas are produced per gram of gas generant. The result is typically a smaller and less expensive inflator due to reduced manufacturing complexity.
Yet another concern is that the compositions must exhibit burn rates that are satisfactory with regard to use in vehicle occupant protection systems. In particular, compositions containing phase stabilized ammonium nitrate may exhibit relatively lower burn rates requiring various measures to improve the burn rate. Accordingly, the development of energetic fuels is one ongoing research emphasis whereby the less aggressive burn characteristics of preferred oxidizers such as phase stabilized ammonium nitrate are accommodated.
U.S. Pat. No. 5,439,251 to Onishi et al. describes 5,5′-bi-1H-tetrazole (BHT), a bi-tetrazole, as potentially decomposing during powdering, or exploding at the time of loading. Onishi explains that this is due to the high impact and friction sensitivities of BHT. The present inventors also note that bi-tetrazoles such as BHT, bis-tetrazole amine (BTA), and 5,5′-azobis-1H-tetrazole (ABHT) are believed to be corrosive with regard to the various constituents of known airbag gas generators for example. Onishi solves the problem of sensitivity by forming amine salts of bi-tetrazoles that are not so disadvantaged.
U.S. Pat. No. 5,872,329 describes amine salts of bi-tetrazoles including salts of BHT and ABHT. Again, these salts are recognized for their usefulness as fuels in gas generating compositions for gas generators, particularly due to their relative insensitivity as compared to the acidic bi-tetrazoles mentioned above, for example.
U.S. Pat. No. 6,210,505 again describes gas generating compositions containing the amine salts of bi-tetrazoles of U.S. Pat. No. 5,872,329 and phase stabilized ammonium nitrate (PSAN). However, '505 recognizes that the amine salts of bi-tetrazoles when combined with PSAN have reduced energy as compared to the base bi-tetrazoles BHT and ABHT, for example. The resulting less-than-optimum burn rates of these compositions requires the use of a much more robust inflator, with the attendant increased manufacturing costs. To address this concern, metallic oxidizers, and other metal-containing constituents such as clay, are added to improve the burn rates of compositions containing the amine salts of tetrazoles and PSAN, or, to increase the combustion energy of the associated compositions when deployed as gas generating compositions in an airbag gas generator, for example. The addition of metallic oxidizers and other metal-containing constituents, however, produces increased solids and requires increased filtration of the effluent. This typically increases the weight of the associated gas generator.
It would therefore be an improvement in the art to be able to utilize bi-tetrazoles because of advantageous gas production, while yet avoiding the concerns described above.